RNA interference (RNAi) is the process whereby double-stranded RNA (dsRNA) induces the sequence-specific degradation of homologous mRNA. Although RNAi was first discovered in Caenorhabditis elegans (Fire et al., 1998), similar phenomena had been reported in plants (post-transcriptional gene silencing [PTGS]) and in Neurospora crassa (quelling) (reviewed in Hammond et al., 2001; Sharp, 2001). It has become clear that dsRNA-induced silencing phenomena are present in evolutionarily diverse organisms, e.g., nematodes, plants, fungi and trypanosomes (Bass, 2000; Cogoni and Macino, 2000; Fire et al., 1998; Hammond et al., 2001; Ketting and Plasterk, 2000; Matzke et al., 2001; Sharp, 2001; Sijen and Kooter, 2000; Tuschl, 2001; Waterhouse et al., 2001). Biochemical studies in Drosophila embryo lysates and S2 cell extracts have begun to unravel the mechanisms by which RNAi works (Bernstein et al., 2001; Tuschl et al., 1999; Zamore et al., 2000).
Although work has been done generally in the area of RNAi, there is a need for further study of such systems. Moreover, there exists a need for the development of reagents suitable for use in vivo, in particular for use in developing human therapeutics.